Update: Release has been postponed until tomorrow (Friday, October 3rd) due to technical difficulties. When released, you will be able to find the mods in the "uninstalled" section of your "My games" tab within Steam.

This Thursday is big. For the first time ever, mods will be delivered through Valve's digital distribution platform thus opening up new opportunities to both mods and Steam alike. Five different mods were selected to be integrated using Steamworks which helps streamline the delivery, installation, and update process. Some of the mods will even have other features like achievements and stat tracking, with others gaining added functionality in future updates. The majority of mods selected also have significant content updates, so be sure give them all a shot. Automatic installation means you have no excuse not to!

For the uninitiated, here's a quick look at the five mods that are the first to make their way onto the Steam platform:

Car combat on the Source engine. Rain down destruction on your opponents in the form of high explosives and machine gun fire. A wide variety of maps with plenty of destructibility. Almost no learning curve makes this mod easy to pick up and play.

A realistic modern warfare shooter set within the middle east. Play as conventional military forces or the underground insurgents. Employ tactics and teamwork to capture objectives while holding out against enemy reinforcements.

The best Half-Life 2 co-op experience out there. Melded together from a smattering of smaller co-op mods. Play through custom campaigns or the entire Half-Life 2 campaign cooperatively with new features, weapons and NPCs.

The most popular Zombie mod on the Source engine. One person starts as the undead and gains new teammates with every survivor killed. Survivors must hold out against diminishing odds and constant paranoia... or find a really good hiding place.

ModDB extends its congratulations to all the mod teams involved. We hope that this allows for even more people to experience and enjoy the products of your creative endeavors.

It's just another downloadable file, so why would it be easier to check for updates if a certain game uses the Source-engine? Nonsense..
Also, there are many games on steam, which don't use the Source-engine.

Why wouldn't they? As another commentor said, it's just as easy to implement updates among other things. Were talking about Valve not EA. A company who has openly supported indie gaming many times, (especially with the release of steamworks). They will most likely do this in the future for non-valve made game mods.

I dunno. ZPS seems very uninspired to me - it's really only slightly better than the CS or GM zombie survival mods, and only because it's a separate full polished mod rather than somewhat of a hack like the other two. Gameplay wise there isn't a huge difference.

Zombie Master will forever be my favorite, it's really too bad that they weren't given this opportunity.